Pollination

1 Mark Questions

1. What is pollen-pistil interaction and how is it mediated? [Foreign 2014]

Ans. Pollen-pistil interaction is a chain or group of events that takes place from the falling of pollen over the stigma to the formation of pollen tube and its entry into the ovule. It is basically the phenomenon of acceptance or rejection of pollen grains by the pistil (stigma), which is mediated by chemical components of pollen grain, interacting with that of pistil,

2.Differentiate between xenogamy and geitonogamy? [Delhi 2014 c]

Ans. Xenogamy is transfer of pollen grains from anther of one flower to stigma of another flower of a different plant, while geitonogamy is transfer of pollen grains from anther of one flower to stigma of another flower on same plant.

1. How do the pollen grains of Vallisneria protect themselves? [All India 2012]

Ans. As the pollination of Vallisneria takes place by means of water, the pollen grains are covered by mucilaginous coating that protects them

1. Why do the pollen grains of Vallisneria have a mucilaginous covering? [hots; Delhi 2010]

Ans. In Vallisneria, the male flowers are released on the water surface. So, to provide protection to these pollen grains, a mucilaginous covering is present. True hydrophily can be seen in Vallisneria.

1. Mention the pollinating agent of an inflorescence of small dull coloured flowers with well

exposed stamens and large feathery stigma. Give any one characteristic of pollen grains produced by such flowers. [Delhi 2009]

Ans. The pollinating agent in the described inflorescence with small dull coloured flowers having well exposed stamens and large stigma is wind. The pollens are non-sticky and can be easily dispersed by wind currents and so large, feathery stigma easily traps air borne pollen grain.

For example, corn cob, its ears or silk (stigma and style) wave in the wind to trap pollen grains.

6.Name the type of flower which favours cross-pollination. [All India 2009]

Ans. Chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma favour cross-pollination.

1. The following statements (i), (ii) and (iii) seem to describe the water pollinated submerged plants. Which one of these statements is incorrect?

(i)The flowers do not produce nectar.

(ii)The pollen grains have mucilaginous covering.

(iii)The brightly coloured female flowers have long stalk to reach the surface. [Foreign 2009]

Ans. Statement (iii) is incorrect. As in submerged plants, female flowers remain submerged, while pollen grains are long ribbon-like to reach passively to stigma inside water, so as to achieve pollination.

1. Name the type of pollination as a result of which genetically different types of pollen grains

of the same species land on the stigma.[Foreign 2009]

Ans.Xenogamy/allogamy is the type of pollination as a result of which genetically different types of pollen grains of the same species land on the stigma.

2 Marks Questions

9.In angiosperms, zygote is diploid while primary endosperm cell is triploid. Explain. [All India 2013] or

Mention the reasons for difference in ploidy of zygote and primary endosperm nucleus in an angiosperm. [Delhi 2010]

Ans. In angiosperms or flowering plants, one of the male gamete fuses with egg cell which results in formation of zygote. So, zygote is diploid. While primary endosperm cell is triploid because the nucleus of the second male gamete fuses with the two haploid polar nuclei or diploid secondary nucleus of the central cell to form a triploid primary endosperm nucleus. The central cell is now called primary endosperm cell.

10.State one advantage and one disadvantage of cleistogamy.[All India 2012]

Ans.Advantage and disadvantage of cleistogamy are as follows:

Advantage Cleistogamous flowers produce assured seed-set even in the absence of pollinators.

Disadvantage Cleistogamous flowers are invariably autogamous. So, there is no chance of cross-pollination.

11. Why should a bisexual flower be emasculated and bagged prior to artificial pollination? [Foreign 2010]

Ans. Emasculation in a bisexual flower is required to prevent contamination of the stigma with self pollen grains. Bagging is done to prevent contamination of the stigma of the emasculated flower with any other unwanted pollen grains. That's why a bisexual flower should emasculated and bagged prior to artificial pollination

12.Explain any two devices by which autogamy is prevented in flowering plants. [All India 2009]

Ans. The two devices to prevent autogamy in flowering plants are:

1. Anthers and stigma of a flower are placed in such a way that pollen of the same flower cannot fall on the stigma.
2. Self-incompatibility is a genetic process that prevents germination of pollen from the same flower on the stigma

13.The flower of brinjal is referred to as chasmogamous, while that of beans is

cleistogamous. How are they different from each other? [Delhi 2008]

Ans. Differences between chasmogamous flower of brinjal and cleistogamous flowers of beans are:

Chasmogamous flower Cleistogamous flower These open at maturity These are bisexual and expose their flowers which do not stigma(s) and stamen(s). open at all even in maturity. They may be cross Self pollinated only. pollinated or self pollinated.

14. What is geitonogamy? Give its one similarity to

(i)Autogamy (ii) Xenogamy. [Delhi 2008]

Ans. (i) Geitonogamy is pollen from onethe condition in which flower are deposited on the stigma of another flower borne on the same plant.